1. Field of Invention
This invention is directed to magnetic actuators.
2. Description of Related Art
Actuators are, in general, magnetostatic, electrostatic, or mechanical. Magnetostatic actuators include well known solenoids, in which a coil of wire is energized to create a magnetic field in the interior of the coil which then interacts with a magnetic solid core, to attract the magnetic core into, or repel the magnetic core from, the interior of the coil.
FIG. 1 illustrates an example of a known solenoid actuator 1. A coil of wire 10 is energized by a current I, which produces a magnetic field B within the interior of coil 10. Magnetic core 20 interacts with magnetic field B created within coil 10 such that magnetic core 20 is pulled toward the interior of the coil. As core 20 is drawn into the interior of coil 10, the displacement may be used to actuate other devices such as valves or switches, which may be coupled to magnetic core 20. The solenoid actuator 1, in general, is only applied to devices requiring solid, mechanical actuation.
To actuate fluidic or hydraulic devices, such as droplet dispensers, fluid is forced under pressure through a cylindrical tube and out of an orifice. In the case of relatively large droplet dispensers, droplet formation generally occurs when the force of gravity exceeds the surface tension of the droplet at the orifice. Therefore, for droplet volumes of several hundred nanoliters to 1 microliter or more, droplets can be dispensed by syringe pipettes, for example.
For smaller droplet volumes, kinetic energy must be delivered to the droplet volume sufficient to overcome the surface tension at the point of ejection. Kinetic energy may be imparted by piezoelectric elements or thermal elements, such as those used in ink-jet devices. Typical ink-jet devices are capable of dispensing droplets in the 10 to 100 picoliter range.
However, for droplet sizes in the intermediate range, such as in the range 1 nanoliter to 1 microliter, limited options exist. If it is acceptable to contact the surface which will receive the droplet, then “quill-pen” contact dispensing is possible, wherein a slotted cylindrical tube draws fluid in by capillary force, and dispenses the fluid by contacting the slotted cylindrical tube to a receiving surface. When non-contact dispensers are required, systems are available which pressurize a fluid in a supply volume and provide miniature solenoid switches that switch the fluid pathway between the supply volume and the ejection orifice.